Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.61   5.633%   $262.6142   $262.61   $262.60   $262.60  
  Purchase #2 $226.99   9.487%   $248.5245   $248.52   $248.50   $248.50  
  Purchase #3 $128.31   12.794%   $144.726   $144.73   $144.75   $144.70  
  Purchase #4 $70.60   6.546%   $75.2215   $75.22   $75.20   $75.20  
  Purchase #5 $144.82   4.670%   $151.5831   $151.58   $151.60   $151.60  
  Purchase #6 $95.61   9.340%   $104.54   $104.54   $104.55   $104.50  
  Purchase #7 $209.49   4.763%   $219.468   $219.47   $219.45   $219.50  
  7 purchase totals = $1,124.43       $1,206.6773   $1,206.67   $1,206.65   $1,206.60